1. Field of the Invention
The present invention relates to a method of concentration and separation of .gamma.-linolenic acid esters or arachidonic acid esters by taking advantage of the difference in affinity of highly unsaturated fatty acid esters to zeolites.
2. Description of the Prior Art
.gamma.-Linolenic acid (hereinafter abbreviated to GLA) and arachidonic acid (hereinafter abbreviated to AA) are important materials as precursory materials to prostaglandin and are recently drawing particular attention because of their divergent physiological activities. Particularly, as a result of discovery that GLA or AA can be mass-produced utilizing various species of microorganisms, active research and development have been pursued on them.
Heretofore known as general methods for concentration and separation of GLA and AA from mixtures of fatty acid esters are urea adduct process and silver complex process (both covered by British Pat. No. 1240513); by the former method, the products' purities are low and the urea's cost is high and the latter method also involves high cost of silver; therefore, they both can hardly be said suitable for application on industrial scale. As other potentially effective methods, enzyme method, low temperature fractional crystallization method, supercritical fluid extraction method, molecular distillation method, etc., may be mentioned. With these methods, many defects and technical themes to resolve in the aspects of purity, cost and operation are left and therefore, it is quite difficult to obtain GLA and AA at high purity on industrial scale.